Performance of a Sensitive Micromachined Accelerometer With an Electrostatically Suspended Proof Mass

A three-axis micromachined accelerometer with a proof mass suspended electrostatically in six degrees of freedom was designed and tested to evaluate its performance of this sensitive sensor for potential microgravity space applications. The device is based on a glass/silicon/glass bonding structure, fabricated by bulk micromachining process, and operated with force-balance technology. The motion of the proof mass with respect to each side is fully servo-controlled by capacitive position sensing and electrostatic force feedback. The design and simulation of multiaxis suspension control loops are presented based on the stiffness requirements for different full-scale ranges. The ground test of this sensitive accelerometer is facilitated by setting the vertical axis at a relatively high measurement range to counteract the one-g gravity, whereas the range in two lateral axes can be set as low as possible to achieve high sensitivity. Detailed experimental results of electrostatic suspension, three-axis accelerometer, and its cross-axis sensitivity are presented with the device operated initially in an atmospheric environment. The preliminary test results of a prototype accelerometer show that a sensitivity up to 688.8 V/g and a noise density down to 3 mu g/Hz(1/2) can be achieved by setting an extremely low full-scale range of +/- 2.90 mg. The results also show that much different stiffness levels in the design of three-axis suspension is a major source of cross coupling effects in the prototype accelerometer.